This invention relates to apparatus for pulverizing, i.e., grinding, material, and more specifically to an auxiliary lubrication system that is particularly suited for use with a pulverizer bowl mill whereby the auxiliary lubrication system is operative to supplement the pulverizer bowl mill's existing lubrication system by supplying filtered oil to the main shaft bearings of the drive of the pulverizer bowl mill.
It has long been known in the prior art to provide apparatus employable for purposes of effecting the grinding of materials. More specifically, the prior art is replete with examples of various types of apparatus that have been used heretofore to effect the grinding of a multiplicity of different kinds of materials. In this regard, in many instances discernible differences of a structural nature can be found to exist between individual ones of the aforesaid apparatus. The existence of such differences is, in turn, attributable for the most part to the diverse functional requirements that are associated with the individual applications in which such apparatus are designed to be employed. For instance, in the selection of the particular type of apparatus that is to be utilized for a specific application, one of the principal factors to which consideration must be given is that of the nature of the material that is to be ground in the apparatus. Coal is one such material wherein there is a need to grind it in order to render it suitable for use in certain applications. Furthermore, fossil fuel fired power generation systems represent one such application in which it is desired to employ coal, as the source of fuel therefor, and wherein a requirement exists to grind, i.e., pulverize, the coal to render it suitable for use for this purpose, i.e., for use in a coal-fired power generation system.
For purposes of the discussion that follows, the coal-fired power generation systems referred to above are considered to consist of essentially the following major operating components: a coal feeder, apparatus for pulverizing coal, a distribution system for distributing the coal after the pulverization thereof, a furnace in which the coal is to be burned and the requisite controls for effecting the proper operation of the coal-fired power generation system. Of particular interest herein is that portion of the coal-fired power generation system which has been identified above as the apparatus for pulverizing the coal. Coal pulverizing apparatus are not new. They have been known to exist in the prior art for more than half a century. Furthermore, many improvements in the construction and/or mode of operation of coal pulverizing apparatus have been made during this period.
There are a number of features that it is advantageous for many coal pulverizing apparatus to possess, but particularly those which are designed for employment in a coal-fired power generation system. Reference is had here to features such as reliability, low power consumption, minimum maintenance and wide range of capacity. In addition, such apparatus advantageously should also be characterized by quiet operation, integrated lubrication systems, convenient adjustment and control of coal flow and fineness, and the ability to handle the high temperature air that is required for high moisture coal.
One particular type of coal pulverizing apparatus which is to be found in the prior art that is advantageously characterized by the embodiment therein of the above-recited features is an apparatus most commonly referred to in the industry by the name bowl mill. The latter apparatus obtains its name by virtue of the fact that the pulverization, i.e., grinding, of the coal which takes place therein is effected on a grinding surface that in configuration bears a resemblance to a bowl.
Reference may be had, by way of exemplification, to U.S. Pat. No. 3,465,971, the latter being assigned to the same assignee as the instant application, for a teaching of the nature of the construction and the mode of operation of a prior art form of bowl mill that is suitable for use in a coal-fired power generation system to effectuate the pulverization of the coal that is to be burned as fuel therein. As taught by the aforementioned patent, a bowl mill essentially consists of a body portion in which a grinding table is mounted for rotation, a plurality of grinding rollers that coact with the grinding table to effect the grinding of coal interposed therebetween, coal supply means for feeding to the interior of the bowl mill the coal that is to be pulverized, and air supply means for supplying to the interior of the bowl mill the air required in the operation of the latter. In accordance with the mode of operation of such a bowl mill, the coal, which enters the bowl mill, is pulverized by virtue of the coaction of the grinding rollers with the grinding table. After being pulverized, the coal particles are thrown outwardly by centrifugal force whereby the particles are fed into a stream of air that is entering the bowl mill. The stream of air, which now contains pulverized coal particles, flows through a tortuous path that is established in part by the positioning within the bowl mill of a suitably supported deflector means. As the stream of air and coal particles flows along the aforementioned tortuous path, the sharp turns contained therein effects the separation of the coarse coal particles from the air stream. These coarse coal particles are then suitably returned to the grinding table for further pulverization while the fine coal particles are carried through the bowl mill in the air stream, and exit therefrom along with the air.
In a conventional coal-fired power generation system, a multiplicity of bowl mills of the type shown in the aforementioned patent would commonly be employed for purposes of satisfying the requirements of the system for pulverized coal. By way of example, the capacity of each of the individual bowl mills might be on the order of one hundred tons per hour of coal.
Although bowl mills constructed in accordance with the teachings of the aforementioned patent have, under actual operating conditions, proven capable of providing adequate performance to date a need has nevertheless been evidenced for improvements to be made therein. More specifically, prolonged operation of this type of bowl mill has revealed the existence of several conditions of an undesirable nature that can arise during the use thereof. In particular, reference is had here to the fact that prior art forms of lubrication systems for pulverizing bowl mills are known to suffer, by way of exemplification and not limitation, from the following disadvantages. One of these is that such prior art forms of lubrication systems for pulverizing bowl mills embody no provision for filtering contaminants from the lube oil. Another is that such prior art forms of lubrication systems for pulverizing bowl mills embody no provision for high volume purging flow through the lower bearings of the pulverizing bowl mill wherein such high volume purging flow is designed to be operative to inhibit contamination accumulation in this area. A third is that in accord with the mode of operation of such prior art forms of lubrication systems for pulverizing bowl mills oil is pumped to the upper bearing of the pulverizing bowl mill only when the pulverizing bowl mill is operating. A fourth is that in accord with the mode of operation of such prior art forms of lubrication systems for pulverizing bowl mills oil volume flow is inherently limited by the nature of the pump design thereof to the extent that cooling rates recommended by the bearing manufacturer can not be satisfied therewith. A fifth is that when employed under certain conditions it takes considerable time for such prior art forms of lubrication systems for pulverizing bowl mills to confirm by means of the visual sight gauge the existence of upper bearing return oil flow in the pulverizing bowl mill, such confirmation being required before the material that is to be ground in the pulverizing bowl mill can be admitted to the pulverizing bowl mill. A need has, therefore, been evidenced in the prior art for a new and improved form of lubrication system suitable for use with a pulverizing bowl mill which by filtering out wear causing oil contaminants would enable bearing and gear life to be extended thereby eliminating costly premature replacement of these components, by providing the higher flow rate recommended by bearing manufacturers would reduce upper bearing operating temperature thereby extending bearing life, by continuously purging the lower bearing area within the pulverizing bowl mill would reduce the accumulation of contaminants in the aforesaid area thereby lessening the potential for premature thrust and lower radial bearing failures, by maintaining oil cleanliness would reduce lubricant replacement cost, by employing on-line filtration which is more effective would eliminate the labor costs associated with periodic cleanup using portable equipment, and by pumping oil to the upper bearing continuously, i.e., even when the pulverizing bowl mill is not operating, would enable the material that is to be ground in the pulverizing bowl mill to be admitted thereto immediately after the pulverizing bowl mill is started thereby obviating the need to wait the time which would otherwise be required in order to confirm by means of the visual sight gauge the existence of upper bearing return oil flow in the pulverizing bowl mill before admitting thereto the material that is to be ground therein. To thus summarize, a need has been evidenced in the prior art for such a new and improved lubrication system suitable for use with a pulverizing bowl mill which would be operative to enable an enhancement of the availability of the pulverizing bowl mill to be realized without necessitating additional operating requirements or restraints.
It is, therefore, an object of the present invention to provide a new and improved lubrication system suitable for use with a bowl mill of the type that is operative for effecting therewithin the pulverization of a material such as coal.
It is a further object of the present invention to provide such a lubrication system particularly suited for use with a bowl mill which is operative to supplement the bowl mill's existing lubrication system by supplying filtered oil to the main shaft bearings of the bowl mill.
It is another object of the present invention to provide such an auxiliary lubrication system particularly suited for use with a bowl mill which is characterized in that by filtering out wear causing oil contaminants bearing and gear life is extended such that costly premature replacement of these components can be eliminated.
It is still another object of the present invention to provide such an auxiliary lubrication system particularly suited for use with a bowl mill which is characterized in that by providing the higher flow rat recommended by bearing manufacturers the upper bearing operating temperature is reduced thereby enabling bearing life to be extended.
A further object of the present invention is to provide such an auxiliary lubrication system particularly suited of use with a bowl mill which is characterized in that by continuously purging the lower bearing area within the bowl mill accumulation of contaminants in this area is reduced thereby lessening the potential for premature thrust and lower radial bearing failures.
A still further object of the present invention is to provide such an auxiliary lubrication system particularly suited for use with a bowl mill which is characterized in that by maintaining oil cleanliness a reduction in lubricant replacement cost can be realized.
A still another object of the present invention is to provide such an auxiliary lubrication system particularly suited for use with a bowl mill which is characterized in that by pumping oil to the upper bearing continuously, i.e., even when the pulverizing bowl mill is not operating, enables the material that is to be ground in the pulverizing bowl mill to be admitted thereto immediately after the pulverizing bowl mill is started rather than having to wait until the existence of upper bearing oil flow in the pulverizing bowl mill is confirmed by means of the visual sight gauge before the material that is to be ground in the pulverizing bowl mill can be admitted thereto.
Yet a further object of the present invention is to provide such an auxiliary lubrication system particularly suited for use with a bowl mill which is characterized in that by employing on-line filtration which is more effective the labor costs associated with periodic cleanup using portable equipment are eliminated.
Yet another object of the present invention is to provide such an auxiliary lubrication system particularly suited for use with a bowl mill which is designed for employment primarily in retrofit applications.
Yet still another object of the present invention is to provide such an auxiliary lubrication system particularly suited for use with a bowl mill which is advantageously characterized by its ease of manufacture and its ease of assembly in cooperative association with a bowl mill, as well as by the fact that it is relatively inexpensive to provide.